Passive girdle for heart ventricle for therapeutic aid to patients having ventricular dilatation

ABSTRACT

A passive girdle is wrapped around a heart muscle which has dilatation of a ventricle to conform to the size and shape of the heart and to constrain the dilatation during diastole. The girdle is formed of a material and structure that does not expand away from the heart but may, over an extended period of time be decreased in size as dilatation decreases.

This invention is a continuation-in-part of U.S. patent application Ser.No. 08/490,080 filed Jun. 13, 1995. The contents of patent applicationSer. No. 08/490,080 are specifically incorporated herein by reference.

BACKGROUND OF THE INVENTION

Patients having a heart condition known as ventricular dilatation are ina clinically dangerous condition when the patients are in an end stagecardiac failure pattern. The ventricular dilatation increases the loadon the heart (that is, it increases the oxygen consumption by theheart), while at the same time decreasing cardiac efficiency. Asignificant fraction of patients in congestive heart failure, includingthose who are not in immediate danger of death, lead very limited lives.This dilatation condition does not respond to current pharmacologicaltreatment. A small amount, typically less than 10%, of the energy andoxygen consumed by the heart, is used to do mechanical work. Thus thebalance, which is the major part of the energy consumed by the heart isused in maintaining the elastic tension of the heart muscles for aperiod of time. With a given pressure, the elastic tension is directlyproportional to the radius of curvature of the heart ventricle. Duringventricular dilatation the ventricular radius increases and the energydissipated by the heart muscle just to maintain this elastic tensionduring diastole is abnormally increased, thereby increasing oxygenconsumption. A number of methods and devices have been employed to aidthe pumping action of failing hearts. Many of these include sacs orwraps placed around the ailing heart, or, in some instances only aroundthe ventricle of the failing heart, with these wraps constructed toprovide for active pumping usually, but not always, in synchronism withthe ventricular pumping of the natural heart. Table 1 lists a number ofdeveloped devices with pertinent operating characteristics.

                                      TABLE 1                                     __________________________________________________________________________          Level of       Blood                                                    Device                                                                              Support                                                                           Pulsatility                                                                         Duration                                                                           Contanting                                                                           Comments                                          __________________________________________________________________________    IABP  Partial                                                                           Y     Days to                                                                            Y      Counterpulsation                                        <20%      Months      provides LV unloading                             Biopump                                                                             Full                                                                              N     Days Y      Limited to short                                                              duration due to                                                               thrombotic potential                              Thoractec                                                                           Full                                                                              Y     Months                                                                             Y      Sac-type actuation                                Novacor                                                                             Full                                                                              Y     Months                                                                             Y      Sac-type pump with                                                            electric actuation                                Hemopump                                                                            Partial                                                                           N     Days Y      Axial flow pump                                         50-75%                                                                  Heart Mate                                                                          Full                                                                              Y     Months                                                                             Y      Pusher-Plate pneumatic                                                        and electric                                      Aortic Patch                                                                        Partial                                                                           Y     Months                                                                             Y      Counterpulsation                                  BVS 5000                                                                            Full                                                                              Y     Weeks                                                                              Y      Designed for temporary                                                        support                                           Anstadt                                                                             Full                                                                              Y     Days N      Cardiac resuscitation                             Cardio-                                                                             Partial                                                                           Y     Years                                                                              N      Requires muscle                                   myoplasty                                                                           <20%                  training                                          __________________________________________________________________________

One, more recent development involves the wrapping and pacing of askeletal muscle around the heart to aid in the pumping. In thatconfiguration, a pacemaker is implanted to control the timing of theactivation of the wrapped around skeletal muscle.

It is an object of this invention to provide a completely passive girdleto be wrapped around a heart suffering from ventricular dilatation tolimit this dilatation and thus improve the performance characteristicsof the heart.

It is another object of this invention to provide a passive girdle orvest which can, over a period of time, have its diameter decreased toeffect some decrease in dilatation of the ventricle.

Other objects will become apparent in accordance with the description ofthe preferred embodiments below.

SUMMARY OF THE INVENTION

Ventricular dilatation is a clinically dangerous condition for end stagecardiac failure patients. The output of the heart is effected by: (a)end-diastolic volume (ventricular volume at the end of the fillingphase), (b) end-systolic volume (ventricular volume at the end of theejection phase), and (c) heart rate. When (a) is very large, (b) alsotends to be larger and (c) tends to be larger than normal. All three ofthese factors contribute to large increases in the tension-time integraland therefore to increased oxygen consumption.

Only a small amount of the energy consumed by the heart is used to domechanical work. For example, with a cardiac output of 5 liters/minute,and Δp of 100 mm(Hg), the mechanical work done by the left ventricle isabout 1.1 watts, and that of the right ventricle is about 0.2 watts.This compares with the typical total energy consumed by the heart(mechanical work during systole plus the energy cost in maintainingelastic tension during diastole) of about 12 to 15 watts.

Thus, since cardiac efficiency (typically between 3% and 15%) is definedas the ratio of the mechanical work done by the heart to the totalenergy (or load of the heart muscle): then,

Cardiac Efficiency, ##EQU1## P_(v) : Ventricle Pressure P: Pressure

V: Volume

T: Tension

t: Time

The constant k accounts for conversion of units.

An increase in mechanical work by a large factor results in a smallincrease in oxygen consumption but an increase in tension time causes alarge increase in oxygen consumption. Patients with dilated ventricleswho have undergone active cardiomyoplasty have not been reported to showany objectively measurable hemodynamic improvement.

Broadly speaking in the present invention a completely passive girdle iswrapped around the ventricle or the entire heart muscle, and sized sothat it constrains the dilatation during diastole and does not effectthe action of the ventricle during systole. With the present surgicaltechniques, it is expected initial access to the heart to place thegirdle in position, will require opening the chest. However, it may bepossible to locate a girdle in position without thoracotomy. In oneembodiment, a synthetic girdle made from material that can limittension, but is otherwise deformable to conform to the anatomicalgeometry of the recipient heart is used. This girdle may be adjustablein size and shape over an extended period of time in order to graduallydecrease the ventricular dilatation. A second embodiment employs a fluidfilled passive wrap constructed of a series of horizontal sections. Thisprovides for a variable volume to be enclosed by the wrap with volumecontrol being obtained by controlling the volume of fluid from animplantable reservoir within the body. In its most preferable form, thispassive wrap can be formed of a series of horizontal tubular segmentseach individually sealed and attached to one another along the long axisof the cylinder. If the cylinders are made of indistensible material,then changing the volume of fluid from the cylinders being in asubstantially deflated condition to one where they are partially orfully inflated, decreases the internal perimeter of the wrap or girdle,thereby decreasing the effective radius of the girdle around the heart.Another feature of the invention is a feedback system, wherein sensors,for example, strain gauges, can be built into an indistensible lining tomeasure its tension and thereby provide automatic feedback to ahydraulic circuit controlling the wrap volume.

To avoid the problem of potential irritability and damage to theexternal myocardium cells by virtue of the artificial wrap and its longterm constraining contact with the myocardium, one embodiment of theinvention employs a tissue engineered lining to protect the myocardium.This tissue engineered lining consists of a polymer scaffold seeded withmyocardial cells harvested from the patient's own myocardium usingtissue engineering technology. That lining then generates a biologicalmyocardio-interfacing surface and remains firmly attached to the polymerinterfacing with the surface from which the wrap is made. Such a liningwould integrate biologically to the heart's myocardial cells in a manneranalogous to other devices currently being investigated which use cellscaffolds for in vitro and in vitro tissue engineering.

DESCRIPTION OF THE DRAWINGS

In the drawing:

FIG. 1A is an illustration generally in cross sectional form of a heartgirdle constructed in accordance with the principles of this invention;

FIG. 1B is an illustration in cross-sectional form of the heart girdleof FIG. 1A with the girdle in a pneumatically filled condition;

FIG. 2 is a perspective view of the heart girdle of FIGS. 1A and 1Bshowing the horizontal segments.

FIG. 3 is an illustration generally in block diagram form of a controlsystem for the heart girdle of FIG. 1 including a strain gauge andelectronic actuator to maintain constant tension at the interfacebetween the girdle and the heart muscle;

FIG. 4 is an illustration in perspective view of a heart girdleemploying a flexible mesh of interlocked circular plastic loops;

FIG. 5 is an illustration of a portion of a girdle constructed generallyin accordance with the girdle construction of FIG. 4, but furtherincluding strings adapted to draw the girdle into decreasing diametershape; and

FIG. 6 is another embodiment of a portion of a passive girdle formed ofa material characterized by a specific internal structure; and

FIG. 7 is a cross sectional drawing of a girdle-myocardium interfaceconstructed of biologically engineered myocardial tissue.

DESCRIPTION OF PREFERRED EMBODIMENTS

In FIGS. 1A and 1B there is illustrated one embodiment of a girdle forwrapping around a heart to constrain dilatation of the ventricle andlimit the amount of energy and oxygen required to maintain the heartmuscle in tension.

In FIG. 1A the natural heart 10 is shown with the left ventricle 12somewhat dilated and with a girdle 17 surrounding both the leftventricle 12 and the right ventricle 11. The girdle 17 is formed asillustrated in FIG. 2, with a series of horizontal segments 13a-13iencircling the heart 10, the segments toward the apex of the heart beingsmaller in cross section and in length. The girdle segments 13 arefilled with hydraulic fluid which is maintained at a constant volumeduring the beating of the heart. In this arrangement the girdle isentirely passive and a distensible girdle lining 18 conforms to theshape of the heart at the myocardium girdle lining interface by virtueof the pressure of the fluid filled segments 13 against the distensibleinner lining 18. As shown in FIG. 3, when this girdle is implantedaround a natural heart the volume is controlled through a three-wayvalve 27 which controls the amount of fluid supplied to the girdlesegments 13 from reservoir 25, which is formed of a rigid casing 24.

According to equation (1), it can be seen that an increase in mechanicalwork by a large factor results in a small increase in oxygenconsumption, but an increase in tension time causes a large increase inoxygen consumption. Passive girdling of the heart, as illustrated inFIGS. 1-3, acts to limit or reduce the ventricular size of the diseasedventricle. Over an extended period of time, which may be days or weeks,the fluid 14 volume may be increased, thereby decreasing the peripheryof the interface lining 18 of the girdle, which may over a period oftime actually decrease the dilatation of the ventricle 12.

In FIG. 3 a control system for controlling the fluid pressure in thesegments 13 according to the tension in liner 18 is shown. The fluidpressure in girdle 13 is controlled by a feedback loop including astrain gauge 42 placed at the interface between the inner lining 18 andthe myocardium providing a sensed value for the tension of themyocardium, to hydraulic actuating electronics 22 which may be aconventional hydraulic control circuit. The electronic actuator 22controls a conventional mechanical fluid actuator 23 which provides forincrease or decrease of fluid within the girdle 17. This actuatoroperates in conjunction with a three-way valve 27 and fluid reservoir25. The change in volume effected by this feedback, is not intended to,nor does it operate in the time frame of the beating of the naturalheart. It is meant to adjust the volume over a much longer time period,typically days, weeks or months.

In this configuration, the series of generally cylindrical segments 13are typically formed of non-distensible material. They are attached toone another along the long axis of the cylinder and may be filled withfluid either individually or in parallel. When the fluid volume withinthe compartments 13 is very low, then the girdle 13 assumes the shapeshown in FIG. 1A providing for a large inner diameter. On the otherhand, when the fluid volume is increased the segments assume, at fillinflation, a circular cross section thereby decreasing the innerperimeter very substantially, as illustrated in FIG. 1B. Thus, bycontrolling the volume of the fluids supplied to the individual segments13, the inner diameter of the girdle 17 can be adjusted to be a closefit to the natural heart. This configuration has the advantage that,since there is no single vertical compartment, there is no gravitypooling of fluid in one portion of the girdle 17.

FIG. 4 illustrates a second embodiment of this invention. The girdle 30of FIG. 4 is an adjustable girdle made from a synthetic material thatcan limit tension, but is otherwise deformable to conform to theanatomical geometry of the heart. In this case, the girdle 30 is formedof a confining net 32 which is wrapped around the heart from the apex tothe atrioventricular (A-V) groove. The purpose of this net is to limitthe maximum diastolic dimension of the heart, while offering noresistance to systolic ejection. In the design illustrated in FIG. 4 anumber of interlinked two-dimensional loops such as lightweight plasticrings 33 are interconnected to form the girdle or wrap 30. The loops 33are free to move in all directions without restraint, since none arephysically connected to each other. Rather, they are interlocked byhaving the loops or rings 33 pass through one another. The design ofFIG. 4 presents no systolic load to the contracting heart. The loop-mesh32 can readily conform to the shape of the heart with the change insurface area accompanying the heart contraction readily accommodated bythe free loops.

An alternative form of this loop-mesh girdle is shown in FIG. 5. In FIG.5 a string system 34 is included with the string attached to the loops33 to effect change in the size of the mesh by virtue of pulling thestrings. This arrangement is able to accommodate a treatment modalityfor scheduled size reduction to the heart over a suitable period oftime. In FIG. 5, a segment of the girdle or wrap 30 is shown. Theoriginal size of the wrap can be seen at the wide edge 36, while thenarrowed down section is seen at the ridge 38 of the wrap. Pulling onthe two ends of two sets of strings reduces the size of the mesh in twodirections. This can be done during a thoracoscopy or through acutaneous access port. In the construction illustrated in FIGS. 4 and 5the net 30 will be attached at several attachment points, typically 4 to6 in number, at the A-V groove and also perhaps near the apex of thenatural heart. At the original implant the surgeon will optimize the fitto the heart as it is existing and will adjust the size through themechanism described above. This design will accommodate spontaneousheart size reduction even though some parts of the mesh may adhere tothe epicardium. However, due to relative motion between the loops, it isunlikely that the mesh will become fully encapsulated. In FIG. 6 thereis shown a girdle in accordance with this invention which is formed of asheet of an expanded poly tetrafluroethylene material 24, prestressedsuch that it remains below its elastic limit and its tension in theplane of the sheet is sufficient to create radially inward forces, thusresisting expansion while permitting inward compression. In other wordsthe girdle will resist further expansion while fittingly accommodatingshrinkage. Other materials may be employed, provided that they exhibitthe above elasticity characteristics.

In FIG. 7 there is illustrated a cross sectional view of a tissueengineered girdle lining having a polymer scaffold 31 which has beenseeded with myocardial cells harvested from the recipient mounted on apolymer substrate 31, the substrate either facing a girdle structure orforming the inner surface of that girdle. The tissue engineered liningfaces the patient's myocardium. Such a lining reduces the irritationwhich may occur between the epicardium and artificial materials employedto form the girdle itself. The lining 30 would, over time, integratebiologically to the patient's myocardium.

Techniques for cell scaffold engineering are described in theliterature. Two examples being, Biodegradable Polymer Scaffolds forTissue Engineering by Lisa E. Freed, Gordana Vunjak-Novakovic, Robert J.Biron, Dana B. Eagles, Daniel C. Lesnoy, Sandra K. Barlow and RobertLanger and Tissue by Robert Langer and Joseph P. Vacanti, Biotechnology,Vol. 12, July 1994 and Tissue Engineering, Robert Langer and Joseph P.Vacanti, Science, Vol. 260 14 May 1993.

This tissue engineering techniques may also be employed with respect toother artificial materials which come in contact with the heart invarious surgical situations including the active devices described inU.S. patent application Ser. No. 08/490,080, filed Jun. 13, 1995.

Having described the above specific embodiments of this invention, otherembodiments implementing the concepts of this invention will doubtlessoccur.

We claim:
 1. A method for treatment of a patient, whose heart ischaracterized by ventricular dilatation comprising the steps of,wrappinga girdle around at least the ventricle of said patient's heart, saidgirdle being wrapped such that it can adjust in size and shape tofacilitate a gradual reduction in the size of the heart; and maintainingsaid girdle in a passive state for an extended period of time, whereinsaid girdle in said passive state conforms to the outer shape of saidventricle and does not expand its dimension in a direction away fromsaid natural heart.
 2. A method in accordance with claim 1 wherein saidgirdle is formed of a sheet of material prestressed in the plane of saidsheet to a value below the elastic limit of said material, said sheethaving a tension which limits extension away from said heart, whileproviding compression forces radially inward toward said heart.
 3. Amethod in accordance with claim 1 wherein said girdle is formed of avertically oriented series of sealed, independent, generallyhorizontally extended cylindrical segments, said vertical orientationbeing parallel with an axis of the heart running to its apex, includingthe further step of,introducing fluid into said cylindrical segments todecrease the inner perimeter of said girdle so that its size conformsgenerally to the size of said patient's ventricle.
 4. A method inaccordance with claim 3 and further including means for increasing thevolume of fluid within said sealed cylindrical segments in a controlledfashion to decrease the dimensions of the inner perimeter when saidventricle decreases in size over an extended period.
 5. A method inaccordance with claim 3 and further including the step of,placing aninner lining between said cylindrical segments and the outer surface ofsaid patient's heart and, placing a tension measuring sensor at theinterface between the outer surface of said patient's heart and theinner lining of said girdle, said sensor providing an output signalindicative of the tension of said lining adjacent to said sensor, and,providing said output signal to means for adjusting the amount of fluidwithin said cylindrical segments until the tension at said lining is ata predetermined value.
 6. A method for treatment of a patient, whoseheart is characterized by ventricular dilatation comprising the stepsof,wrapping a girdle around at least the ventricle of said patient'sheart, providing a scaffold of biologically inert material on saidgirdle and generating a wall on said scaffold by application ofmyocardial cells to said scaffold, said myocardial cells being harvestedfrom said heart, and maintaining said girdle in a passive state for anextended period of time, said girdle being formed such that it canadjust in size and shape to conform to the outer shape of said ventricleand to not expand its dimension in a direction away from said naturalheart.
 7. A method for treatment of a patient, whose heart ischaracterized by ventricular dilatation comprising the steps of,wrappinga girdle around at least the ventricle of said patient's heart; andmaintaining said girdle in a passive state for an extended period oftime, said girdle being formed such that it can adjust in size and shapeto conform to the outer shape of said ventricle and to not expand itsdimension in a direction away from said natural heart during diastolewhile offering no resistance to systolic ejection wherein said girdle isformed of a net of interlocking loops, unattached to one another.
 8. Amethod in accordance with claim 7, wherein said interlocked loops arefurther interconnected by strings extending in at least a firstdimension and including the further step of pulling on said strings todecrease the dimension of said girdle in position around said patient'sheart.